well minus the drifting to the left part, it sounds like a power steering pump... usually when they go out (but not completely) they only work for one way.. that's how my car was... you also end up turning the wheel a bit before it finally kicks in... i.e. the side it works on still kinda jumps around between working and not working...

well i read a little bit more carefully, and i'm still wondering if it isn't the power steering pump... another symptom is it works better when you're car gets moving...

but i've never heard of a power steering problem make the car drift...